The best building tip I ever got... well, this one applies to life in general, I learned it the hard way and I've reminded my son of it as he was growing up, and that is:
Never ever think(or talk) about how good you are at something while you're doing it.

If you are working hard on a project especially when precision is at a premium, and you hear your inner voice say, That'll do, back off and take a break. Come back later when you are fresh and re-think your work.

The best building tip I ever got... well, this one applies to life in general, I learned it the hard way and I've reminded my son of it as he was growing up, and that is:
Never ever think(or talk) about how good you are at something while you're doing it.

I like this one.
And I personally reminded someone of this here, just a few days ago.

A foam roller to varnish a fabric and wood wing in lieu of a brush. The foam roller spreads the varnish (or paint) and if any squeezes thru the fabric the foam will re-absorb it once it when it becomes less saturated with the varnish. Thanks Nigel Tarvin of Tarvin Model Products!

Honestly, the best tip I ever got was from the last guillows kit I attempted to build, believe it or not. Before I started building kits as an adult, I had tried a couple times as a kid and had apparently never noticed the part where you are supposed to put wax paper or plastic wrap over the plans. That was a big Oooooooh thats how this works moment for me